Apparatus for transporting produce under controlled atmosphere



D. A. DIXON 3,269,133 APPARATUS FOR TRANSPORTIN G PRODUCE UNDER CONTROLLED ATMOSPHERE Original Filed April l, 1964 5 Sheets-5heet l A TTOP/VEY f Aug. o0, 1966 D. A. DlxoN 3,269,133

APPARATUS FOR TRANSPORTING PRODUCE UNDER CONTROLLED ATMOSPHERE Orlglnal Filed April l, 1964 5 Sheets-Sheet 2 A T TOP/VE Y Aug. 30, 1966 D. A. DIXON APPARATUS FOR TRANSPORTING PRODUCE UNDER coNTRoLLED ATMOSPHERE 5 Sheets-Sheet S Original Filed April l, 1964 /Blu \\ mw v, V- J ml ...Il 3 Il u Q wv vm o O O y V L o W 4 M 6 o 4 M Vm 4 4 R @d L Q L f .1@ o M /f N/ G 9 H f 3 2 f N 8 w 3 2 f w H 9 M y G H United States Patent O 3,269,133 APPARATUS FOR TRANSPORTING 'PRODUCE UNDER CONTRDLLED ATMUSPHERE David A. Dixon, San Anselmo, Calif., assigner to The Best Fertiiizers Co., Lathrop, Calif., a corporation Original application Apr. 1, 1964, Ser. No. 356,624, now

Patent No. 3,239,360, dated Mar. 8, 1966. Divided and this application Dec. 23. 1964, Ser. No. 420,564

6 Claims. (Cl. 62-51) This application is a division of co-pending application, Serial No. 356,624, tiled April 1, 1964, now Patent No. 3,239,360.

This invention relates to a new and improved apparatus for transporting produce such as fresh fruits and vegetables under a controlled atmosphere. More particularly, the invention provides for rapid, initial reduction in the oxygen content of the compartment sur-rounding the produce to a level set between 1/2% to 4% and then accurately maintaining such low oxygen level for the duration of transportation.

A principal economic loss occurring during transportation of produce, such as fresh fruits and vegetables, is the degradation thereof which occurs between the field and the ultimate destination attributable to the effects of respiration. Heretofore, a conventional attempt to reduce such degradation is to refrigerate the produce to reduce the rate of respiration. One of the important problems which conventional refrigeration does not solve is the inherent time lag which occurs between the original receipt of the produce at its field temperature and the required reduced temperature. A substantial amount of the total degradation of produce occurs during this ltime lag. Accordingly, it is a principal object of the present invention tol greatly decrease respiration during the time between the receipt of produce from the field and its reduction to the refrigeration temperature. This result is accomplished by purging the atmosphere in a refrigerator compartment with a large volume of nitrogen which diffuses throughout the refrigeration compartment, the containers for the produce, and even in the produce itself. The oxygen present in the atmosphere in the refrigerated compartrnent is therefore diluted and displaced and thus reduced to a level set between 1/z% to 4% as contrasted with la level of about 20% in the normal atmosphere. Reduction of the oxygen to a low level, such as 1/2% to 4%, greatly inhibits the rate of degradation of the produce.

Heretofore, other attempts have been made to inhibit initial degradation. One means heretofore employed is precooling the refrigerator compartment, but this requires a source of ice or large refrigeration equipment to accomplish precooling. Another attempts to reduce initial degradation has been vacuum cooling which is accomplished by evacuating the compartment, thereby evaporating a portion of the moisture present in the produce and thus reducing the temperature of the produce. Vacuum cooling, however, requires a centrally located vacuumizing plant. The expense of precooling and vacuum cooling plants and the inconvenience, cost, and delay in transporting the produce to such central plant is eliminated by the present invention.

Incidental to the reduction in the percentage of oxygen by reason of rapid evaporation of nitrogen within the refrigeration compartment is a refrigeration effect atice tributable to the heat of vaporization of the liquified gas. This reduces to a certain extent the workload of the mechanical or other refrigerator but this is not the primary purpose and effect of the emission of nitrogen into the refrigerating compartment. At the present time, one type of refrigeration is accomplished by evaporation of liquied nitrogen into the refrigeration compartment, the rate of introduction and vaporization being governed by temperatu-re within the compartment as distinguished from the percentage of oxygen in the atmosphere as is the case in the present invention. Accordingly, conventional nitrogen refrigeration methods and apparatus do not accomplish the same results as in the present invention, namely, a precise cont-rol of the oxygen level.

As hereinafter set forth in greater detail, after the initial reduction of the oxygen content by purging the cornpartrnent with nitrogen gas, the oxygen is maintained at some chosen level in the range of 1/2% to 4%, usually at about 2%, by means of commercially available equipment which senses the percentage of oxygen and which regulates a valve controlling the delivery of nitrogen into the refrigeration compartment. rlfhus, additional nitrogen is introduced to balance against leakage of outside air into the compartment through the walls and doors of the compartment and, also, to balance the emission of traces of various gases which naturally escape from the produce.

The set level of oxygen is preferably very precisely controlled at a certain percentage, which. varies for different types of produce, but is generally in the range of 1% to 4%. For most produce the level is 2% to 21/2% O2, balance N2. Equipment commercially available will control oxygen level within plus or minus 0.1% of set point under ideal conditions. Inaccuracies in the total system, such as rate of diffusion of N2 and O2, purge convection currents, and the like, reduce accuracy under dynamic conditions to plus or minus 1/2% yof set point; under static conditions to plus or minus 1t%. Green produce at 2% O2 has a respiration rate of one-sixth that at normal atmosphere as contrasted with a respiration rate of one-third normal at 4%. For soft fruits, 31/2% O2 is best and at 1% the danger of anaerobic respiration is great. FIG. l0 is a graph showing effect of variations of O2 level on rate of respiration of produce.

A feature of the invention is the fact that the oxygen level is not brought too low. If the oxygen in the atmosphere is Ibelow certain levels, usually 1%, anaerobic respiration accomplishes serious degradation of the produoc. Accordingly, it is a principal pur-pose tof the present invention to so accurately control the amount of oxygen in the atmosphere that degradation is minimized either fro-n1 oxidation (i.e., respiration) fof the produce or from anaerobic action. Although it has been stated that nitrogen is used in accordance with the present invention, it will further be understood that other inert. gases of which argon is a typical example, may be substituted or mixed. The gases are transported in containers at low temperatures and low pressure in liquid state. An insulation is accomplished to reduce the tendency to evaporate. Such insulation may be accomplished by use of double-walled containers, such as Dewar asks, or by thick layers of insulation.

With some produce, such as lettuce, which is relatively immune to damage from .possible anaerobic respiration, Ioxygen level is sometimes controlled at some point set between and 1%, since certain microorganisms such as molds, bacteria and decay-causing fungi will not grow in such an atmosphere. Usually a further characteristic of such produce is that it is harmed by even trace amounts of carbon dioxide.

In transporting certain produce, of which typical examples are strawberries and apples, the degradation is further reduced by addition of carbon `dioxide to the atmosphere. Accordingly, due to its inhibiting effect on the growth of certain microorganisms, it is contemplated in accordance with this invention that small quantities Iof carbon dioxide may be introduced in addition to the nitrogen and other inert gases.

A further important feature of the present invention is the refrigeration of the compartment during transportation so that the degradation of the produce is further inhibited. In a preferred for-m of the present invention, commercially available compressor-evaporator equipment is installed in the front end of the compartment, assuming the compartment is a trailer or truck, or in another convenient location. Operation of this equipment reduces the temperature of the compartment to a satisfactory level such as about 33 F The capacity of conventional refrigeration equipment of this type for economic reasons is limited so that the temperature of the produce is not brought down immediately, ibut only after the passage of a considerable time. Hence, the initial `degradation heretofore described is not inhibited by this type of refrigeration equipment alone. In fact, -due to the high rate of heat emission of warm produce, at field temperatures, :such in-transit refrigeration equipment is incapable of cooling down produce loaded at eld temperatures when respiration is allowed to proceed in a normal air atmosphere. In accordance with the present invention, the refrigeration equipment merely supplements the inhibition of degradation accomplished by oxygen displacement.

A feature and advantage of the present invention is the use of equipment permitting the gases to be carried in liquid form, thereby maintaining the weight and cost Iof the equipment at a minimum while providing enough gas capacity to emit the large quantities of gas initially required to purge the compartment, as well as to emit lesser quantities of gas over a prolonged period of time while the compartment is being transported to maintain the oxygen level low.

Another feature of the invention is the provision of oxygen and carbon dioxide measuring and level-controlling devices which are rugged and accurate. Such controls may be powered by the gas pressure in the unit and supplemented Iby small batteries for electrical controls which have a long life. Thus, the equipment is essentially self-contained and there is considerable portability between different compartments.

In the preferred form of the apparatus hereinafter described, the equipment, and particularly the nitrogen tank, is carried externally to the refrigeration compartment and thus does not occupy cargo space. As a safety feature, the safety pressure valve of the nitrogen tank is preferably vented to the outside of the compartment, thereby reducing the extreme danger to personnel which arises when the tanks are transported inside the coinpartment and the oxygen level has been reduced below safe conditions for humans by escape of nitrogen through the pressure relief valve. A further safety feature is the use of an oxygen analyzer with a visible indicator gauge vhich warns if the compartment is below a safe oxygen evel.

Another feature of the invention is the provision of a gas supply sufiicient to purge the compartment together with control equipment for the emission of such gas which permits a wide variation in purge rate and thus enables a proper atmosphere to ybe established very rapidly. Further, this system makes practical the use of the invention on substantially all existing produce-hauling trailers, containers and rail cars, without expensive modification, even though they have widely varying air leakage rates. Ac-

cordingly, the present invention can reduce the oxygen level set between 1/2% to 4% within a ten-minute period after the cargo has been loaded into the compartment and the doors closed. Hence, the decomposition of the produce occurs at `full rate only during such ten-minute period and is thereafter greatly inhibited. After the initial purging, the gas supply and the control equipment maintain the oxygen level carefully by a reduced flow of nitrogen. The equipment and controls are such that the ratio between the purge rate and the transportation rate of emission of the nitrogen is in the neighborhood of from 500 to 1.

The present invention has had ioutstanding results in improvement in the condition of produce after transportation. Where oxygen level has been maintained in the neighborhood of 1.% to 4% and the temperature of the compartment has rbeen brought down and maintained in the neighborhood of 35, produce stays fresh and edible up to three times as long as conventional transportation methods. The rate of decline of sugar content, tenderness and fresh appearance of the produce is likewise greatly decreased. Thus the market Value as well as the shelf life of the produce after delivery are lgreatly enhanced. Conversely, where the oxygen in the atmosphere is reduced to the levels indicated, perishable produce lmay be transported under conditions of up to 30 F. higher than optimum transport and storage levels presently prevailing for periods of up to one week without experiencing any more deleterious degradation due to respiration than occurs normally in air under optimum low temperature holding conditions. Accordingly, the present invention provides a cure for the major causes of loss of market value of produce between the field and the terminal market. The invention eliminates the need for -many of the steps of rehandling now necessary between field and the beginning of transportation. It will be understood that much degradation takes place during such -rehandling and hence the present invention has a further benefit in the market value of the produce.

Other objects of the present invention will become apparent upon reading the following specification and referring yto the accompanying drawings in which similar characters of reference represent corresponding parts in each of the several views.

In the drawings:

FIG. 1 is a schematic view of a trailer in which the system of ythis invention is installed at the time of loading cargo.

FIG. 2 is a View similar to FIG. 1, immediately after purging of oxygen.

FIG. 3 is a view similar to FIG. 1, after prolonged refrigeration.

FIG. 4 is an enlarged cross-section through the trailer. FIG. 5 is a view similar to FIG. l, of a modification using CO2 in addition to inert gas.

FIG. 6 is a view similar to FIG. 4, of tem.

FIG. 7 is a View similar to FIG. 4, of a further modified system.

FIG. 8 `is a of FIG. 1.

FIG. 9 is a piping diagram of a modified system.

FIG. 10 is a graph showing, for different kinds of proda modified sysuce, rate of respiration plotted against oxygen level atv constant temperature.

The equipment illustrated in the accompanying drawings is schematic 4and is subject to considerable variation. Essentially there is having ia floor The rear end is preferably closed by doors 17, but doors may be located on the sides. may -be :stationary (as for storage) or may be in the form of a lift van, nevertheless, a common form of compartment is a trailer of the highway 18 and a retractable support 19, and

by a tractor 21 or transported piggy-back on railway piping diagram of one form of the system .provided a cargo compantment 11,` 12, roof 13, sides 14, and front end 16.-

Although compartment 11` type having wheels which may be movedV equipment, or fishy-back on ships. Preferably, the sides 14, ends 16, 17, floor 12, and roof 13, are insulated to reduce heat loss. Particularly where compartment 11 is a highway trailer, the preferred equipment uses ia conventional highway-type refrigerator having a compressor and condenser Z2 installed at the top of front end 16. It will be understood that other mechanical means may be used for refrigeration and other refrigeration means, such as ice or gas evaporation may be used.

Produce, such as crates 23 of fresh fruits and vegetables, is loaded into compartment 11 in normal manner and doors 17 are closed.

In accordance with the present invention, one or `more tanks 26 of liquid nitrogen or mixtures of nitrogen and other gases, such as argon, are used. Tank 26 is supported by brackets 27 extending below oor 12, so that tank 26 extends transversely or longitudinally below floor 12. An auxiliary tank 28 of carbon dioxide may be similarly supponted by brackets 29 (FIG. 5) and used where the presence of such gas in the atmosphere is desirable, as in the transportation of fruits. Tank 26 is, of course, pressure and shock resistant and for such purpose a Dewar fiask is desirable or a metal container suitably insulated with polyurethane lfoam insulation. A pipe 31 runs from tank 26 into compantment 11, preferably to a central location near roof 13 and a plurality of spray holes 32 is formed in pipe 31 so that the liquid rapidly evaporates af-ter emission. Tank 26 has a safety pressure relief valve 33 connected into its head-space which vents gaseous nitrogen to the outside when pressure exceeds a safe level for the strength of tank 26.

The valving equipment `of tank 26 `is likewise subject to considerable variation. As shown in FIG. 8, regulator valve 36 in pipe 31 is controlled by solenoid 37. Mounted in the interior of the compartment is an oxygen sensor 38, a commercially available type of equipment which is :responsive to the percentage of oxygen in the atmosphere to which itis subjected within narrow limits around some set point chosen on meter 39 within 1/2 to 4%. Sensor 38 may be a Beckman polarographic oxygen analyzer, Model 764 (modified), 'as made under Patent No. 2,913,- 386. By means of a relay, or directly through mechanical or electrical connection, sensor 38 controls solenoid 37. Normally, valve 36 is closed 'and is opened only for short periods to emit nitrogen.

In the system shown in FIG. 8, tank 26 is filled through valve 44 with all valves shut except 44. Excess gas pressure will relieve through relief valve 33 only when tank pressure reaches 45 p.s.i.g. Vent valve 41 and vent fitting 40 may be used to remove some or all gas from fthe system or allow faster filling. When the system is turned on by switch 46, an oxygen level reading Ion meter 39 above set point will close meter-relay 48, closing the circuit from source 47 and activating solenoid 37, opening valve 36, allowing nitrogen to fiow up tube 31 to distribution header 32. Before liquid will flow, pressure in the tank must be relieved to p.s.i.g. by back-pressure regulating valve 43. This valve 43 opens whenever pressure upstream exceeds 20 p.s.i.g. and closes whenever upstream pressure falls below 20 p.s.i.g.; its regulation is independent of downstream pressures, thus providing a true economizer circuit. Thus, until valve 43 closes, gas alone, from tank headspace, will ow through tube G to valve 36; after pressure in the tank has been reduced to setting of valve 43, which is considered the working pressure of the system, and valve 43 closes, then liquid nitrogen fiows through Itube L when so called for by the opening of valve 36. Since constant evaporation of liquid nitrogen is occurring within tank 26 due `to healt leak from the outside, this economizer circuit assures that vaporized gas will always be constructively utilized with in the atmosphere control system rather than wasted through relief valve 33. Since in a mov-ing, and thus sloshing tank, head space pressure will build up no faster than the entire bulk of liquid remaining in tank 26 can be brought to equili-brium condition regarding pressure and temperature, considerable stand-by time is possible with this economizer circuit, during which no gas will be lost by relief through valve 33.

If at the time that tank 26 is being filled with nitrogen, produce 23 has already been loaded into compartment 11 land doors 17 have been closed, purge valve 42 is opened instead of vent valve 41 during the filling period, and thus gas that would normally be lost during the filling process is utilized instead for the initial purge of compartment 11.

Tank 26 can be filled through valve 41 and fitting 40 instead of valve 44 and fitting 45 if filling equipment of suitable pressure handling capability is available, and in this case valve 42 is left closed. When filling is completed valve 42 is closed and valve 36 controls thereafter.

An alternate valving system shown in FIG. `9 uses Ian adjustable orifice 50 in line 31a which is adjusted to a size such as to maintain the oxygen level in compartment 11 under normal operating conditions art the desired percentage.

FIG. 9 is similar to FIG. 8 in operation, except that all nitrogen fiowing towards nitrogen iiow control valve 36a, which in this case also serves as the on-off control valve, arrives in gaseous form, and thus all nitrogen fiowing up tube 31a and out of distribution header 32 is in gaseous form. Flow is controlled by an orifice 50, chosen so as to give a constant fiow sufficient to keep oxygen level within 1% of set point in the compartment, i.e., if LZ1/2% oxygen level is desired, then orifice 50 is chosen to give a constant flow rate so that, under the leakage conditions present when using the specific container (compartment) on which this specific system is mounted, oxygen level will stay within the limits of 11/2% to 31/2 It is thus a rougher system than FIG. 8, but simpler, and has the advantage of reliability since electronic devices are not required. Initial purge is accomplished by opening purge valve 42a during filling of tank 26a which filling is normally designed to take place after produce has been loaded into compartment 11 and doors 17 have been closed. If, however, the tank has been filled in advance of loading the compartment with produce, and pressure in tank 26 has during the interim period of time built up to the pressure of the relief valve setting, valve 33a (which in the case of FIG. 9 is set at 60 p.s.i.g. instead of 45 p.s.i.g. as with FIG. 8), the rapid flashing or vaporizing of liquid nitrogen in tank 26a that takes place when the pressure is lowered by opening valve 42a will provide a rapid purge, lalbeit manually accomplished, of the compartment, with the expenditure of about 10% of the total capacity of tank 26a, A slower but automatic purge is accomplished by the fact that if 6() pounds of gas pressure, or some lesser amount down to 20 p..s.i., is applied lagainst orifice Si), flow will be greatly increased over that necessary to maintain steadystate condition within the compartment; thus the same pressure relief phenomenon occurs down to the set pressure of valve 43a, as occurred in the manual purge using valve 42a above, but more slowly. Corresponding parts of the system have the same reference numerals as in FIG. 8, followed by subscript a.

A vaporizer circuit 51, consisting of tubing providing heat exchange between ambient air and liquid nitrogen,

is used to insure that all nitrogen reaches orifice 50 in approximately the same gaseous condition. A strainer 49 protects orifice 50 against being plugged by foreign particles.

In the modification of FIG. 6, tank 26h is mounted inside the compartment 11b. Other elements of the system are designated with the same reference numerals as in the preceding modification followed by the subscript b.

Still another modification is illustrated in FIG. 7, where in oxygen sensor 38C and control equipment, as well as an emission nozzle 46c of the spray type, are installed on the top of tank 26 itself. The unit is thus self-contained and may be installed and removed rapidly. Other elements of this modification are similar to the previous and corresponding parts are marked with the same reference numerals followed by subscript c.

The control equipment by which sensors 38, 38b and 38e regulate valve 36, 36b, 36C, may be actuated by a battery, by a plug-in into the vehicle electrical system, by a combination of a small battery and pneumatic operation pressured by the gas in the container, or by a mechanical -linkage between the oxygen sensor and valve 36. Where electrical means is used, a relay (not shown) is preferably used.

At the commencement of operation, compartment 11 is filled with normal air which has an oxygen percentage of about The temperature of compartment 11 is that of the surrounding air or field temperature which is here assumed to be 80 F. It is also assumed that the temperature of the cargo 23 of produce which is loaded into compartment 11 is at field temperature. This condition is shown in FIG. 1. After loading, doors 17 are closed. An airtight closure is not desirable and it cannot, of course, be achieved in practice with standard refrigeration truck equipment.

After the produce has been loaded, sensor 38 senses excess oxygen 4and opens regulator valve 36 rapidly, emitting into compartment 11 a large volume of nitrogen -as gas or as a liquid, which rapidly Vaporizes into gas and which is approximately seven `or eight times the total volume of the remaining airspace in compartment 11. The nitrogen rapidly diffuses throughout compartment 11, containers 23 for the produce, and into the produce itself. It will be noted that this is a diffusing action and that convection is not essential to the operation. The emission of such a large initial Volume of nitrogen into the compartment purges the atmosphere of air by dilution and expulsion, bringing the oxygen content down to the desired set point between 1/2% to 4%. Preferably, this is accomplished within a time period of about ten minutes. Vaporization of such a large quantity of liquified nitrogen accomplishes a certain amount of refrigeration of the compartment, but because such refrigeration is incidental to the main purpose of the purging of the air by the emission of nitrogen, the temperature as shown in FIG. 2 is still indicated at field temperature of 80 F., although the temperature wou-ld lactually be lower.

After the purging of the compartment, oxidation of the produce due to respiration is greatly reduced and hence the rapid loss of quality of the produce through such degradation is limited to a time period of ten minutes, which is nearlyl lalways sufficiently short that no commercial value is lost.

` After the initial purging of the compartment, compartment 11 may be transported long distances, either by tractor 21 or by railway equipment, or other means heretofore mentioned. Preferably during such transportation, mechanical or refrigeration equipment 22 is operated which reduces the temperature inside compartment 11 to a material extent, such as to the 35 F. indicated in FIG. 3. A cargo temperature range of 33 to 35 is very suitable for most products and this is usually attained over a period of 12 to 72 hours.

Some products, such as lettuce, give longest market shelf life if carried at higher temperature, such as 60 F. Precooled loads also can be loaded, and such condition is preferred when handling soft fruits.

Ice can be the additional refrigerant and in many cases today, particularly when compartment 11 is a railway car, ice is still used to refrigerate produce in transit. When the atmosphere control device is used in conjunction withl the ice refrigeration, t'wo of the great disadvantages of ice refrigeration are overcome: (l) Much less ice is use-d, since in the usual produce haul the heat of respiration, even of a precooled load of produce, is often lthree to six times that of the heat that comes in through the Walls of the container due to heat transmission from outside ambient conditions or suns radiation, and (2) the corallary effect-that of having to stop la train nightly for reicing-is avoided, since one loading of ice at destination will hold the load and handle the remaining refrigeration load all the Way to destination in many cases. It can be seen that the effect of (il) is that of greatly decreased cost, since the cost of ice is quite high 4today compared to what is was when ice cars were rst developed; the effect of (r2) is not only the inherently lesser cost -of using less ice but also the tangible and considerable saving accomplished by not having to stop a train every night of a six-day journey to spend three to six hours reicing all of the cars.

As the transportation or storage of the produce continues, there is a certain amount of leakage of air from the exterior into compartment 11 and, also, certain gases are emitted by the produce. The oxygen sensor 38 senses the presence of oxygen in excess of set point and whenever such percentage is exceeded, an additional quantity of nitrogen is released into the compartment to diffuse through the atmosphere and bring the oxygen le-vel down to the desired range. The quantity of nitrogen normally released in this manner -after the initial purging is relatively small, and hence a tank 26 of liquid nitrogen, or other inert gas, will satisfy all norma-l requirements for transportation for long distances and over prolonged periods of time, such as two weeks.

Sensor 3S likewise maintains the `oxygen level in compartment 11 during transportation above 1/2%, or other level, which inhibits anaerobic degradation of the produce, depending upon the product.

Where desirable, a separate tank 28 of gas such as carbon dioxide may be installed and its emission controlled by a CO2 control means 61 which can be similar to the oxygen control means described hereinabove, cornprising a carbon dioxide sensor means 62 and valve actuating and valve means 63 in the CO2 line 52. The valve means 63 is controlled by the control means in a manner such as to maintain the proper amount -of CO2 gas in compartment `11 for those varieties of produce for which the presence of such gas is desirable, such as soft tree fruits (e.g., peaches), grapes and some other products. CO2 for such products is maintained at some set y point in the range of 3% to 15%.

When the cargo has reached its destination, it will be found that its condition is far superior to that of other means of transportation. Transportation over a two- Week period under these conditions is very satisfactory and more prolonged periods are likewise commercially feasible. v

The term liquified nitrogen has been used herem 1n a generic sense. It will be understood that other gases inert to produce or mixtures may be used. Liquified gases are transported most economically and conveniently and vaporization thereof adds to the effectiveness of the refrigeration system. However, gases in nonliquid form may be used in the sy-stem.

What is claimed is:

1. Apparatus for controlling the oxygen concentration in the atmosphere in a compartment means, comprising:

compartment means adapted to the passage of gaseous atmospheres thereinto and therefrom, equipment means operable to refrigerate said compartment means,

inert gas material source storage means for storing a supply of inert gas material other than oxides of car-bon, to provide a lsource of inert gas material other than oxides of carbon,

passage means having an inlet means communicating with the interior of said source storage means and an outlet means communicating with the interior of said compartment means to allow passage of said inert gas material from the interior of sai-d source st-orage means and out of said outlet means into the interior of said compartment means to become part of said atmosphere in said compartment means,

valve means in said passage means,

oxygen sensing means in said compartment means for `sensing the oxygen concentration in said atmosphere in said compartment means,

valve control means responsive to said oxygen sensing means and connected to control said valve means, whereby Isaid valve means is actuated to permit said inert gas material to flow from said source storage means into the interior of said compartment means to become part of said atmosphere therein when said oxygen sensing means senses oxygen in said atmosphere in said compartment means at a concentration above a predetermined value and to prevent the flow of said inert gas material from said storage means into the interior of said compartment means when `said oxygen sensing means senses oxygen in said atmosphere in said compartment means at a concentration below said predetermined value.

2. The apparatus of claim 1 comprising, in addition:

a second passage means having an inlet means communicating with the interior of said source storage means and an outlet means communicating with the interior of said compartment means to permit introduction of said inert gas material into the interior of said compartment means,

a second valve means in said second passage means.

3. Apparatus for controlling the oxygen concentration in the atmosphere in a compartment means, comprising:

compartment means adapted to the passage of gaseous atmospheres thereinto and therefrom,

equipment means operable to refrigerate said compartment means,

inert gas material source storage means for storing a supply of inert gas material other than oxides of carbon to provide a source of inert gas material other than oxides of carbon,

Ifirst passage means having an inlet means communicating with the lower portion of the interior of said source storage means and an outlet means communicating with the interior of said compartment means to allow passage of said inert gas material from the interior of said source storage means and out of Said outlet means into the interior of said compartment means to become part of `said atmosphere in said compartment means,

first valve means in said lfirst passage means,

second passage means having an inlet means communicating with the upper portion of the interior of said source storage means and an outlet means communicating with the passage in said rst passage means at a point intermediate said source storage means and said first valve means,

second valve means in said second passage means, said second valve means being responsive to the pressure in said source storage means whereby said second valve means permits said stored inert gas material from said source storage means to fiow through said second passage means when said pressure in said source storage means is above a predetermined value and prevents ow of said stored 'inert gas material through said second passage means when said pressure is below said predetermined value,

oxygen sensing means in said compartment means for sensing the oxygen concentration in said atmosphere in said compartment means,

rvalve control means responsive to said oxygen sensing means and connected to control said first valve means, whereby said first valve means is actuated to permit said inert gas material to flow from said source storage means into the interior of said compartment means to become part of said atmosphere therein when said oxygen sensing means senses oxygen in said atmosphere in said compartment means at a in the atmosphere in a compartment means, comprising:

compartment means adapted to the passage of gaseous atmospheres thereinto and therefrom,

equipment means operable to refrigerate said compartment means,

inert gas material source storage means for storing a supply of inert gas material other than oxides of carbon, to provide a source of inert gas material other than oxides of c-arbon,

iirst passage means having an inlet means communicating with the lower portion of `the interior of said `source storage means and an outlet means communicating with the interior of said compartment means to allow passage of said inert gas material from the interior of said source storage `means and Iout of said outlet means into the interior lof said compartment means to become part of said atmosphere in said compartment means,

orifice means in said first passage means to provide a ifiow of inert gas material from said source storage means into the interior of said compartment means at a predetermined rate,

second passage means having inlet means communieating with the upper portion of the interior of said source storage means and outlet me-ans communi* eating with the interior of said compartment means to permit said inert gas material to tiow into said compartment means and become part of said atrnosphere in said compartment means,

first val-ve means in said second passage means, said first valve means when in its open position permitting the ow of inert g-as material through said second passage means into the interior of said compartment means to become part of said atmosphere in said compartment means, and when in its closed position preventing the iiow of inert gas material through said second 1passage means into the interior of said compartment means.

5. The -apparatus of claim 4 comprising, in addition:

third passage means having inlet means communicating with the upper portion of the interior of said source storage means and outlet means communicating with the passage in said first passage means at a point intermediate said orifice means and the interior of said source storage means,

`second valve means in said third passage means, said second valve means being responsive to the pressure -in said source storage means whereby said second valve means permits said inert gas material from `said source storage means to flow through said third passage means when said pressure in said source storage means is above a predetermined value and prevents flow of said inert gas material through said third passage means when said pressure is below said predetermined value.

6. The apparatus of claim 1 comprising, in addition:

CO2 source storage means,

CO2 passage means having inlet means communicating with the interior of said CO2 source storage means and outlet means communicating with the interior of said compartment means,

C02 control means to control the amount of CO2 admitted into the said atmosphere in said compartment means, whereby the concentration of said CO2 in said atmosphere is maintained substantially at a predetermined value. l

(References on following page) i l 1 2 References Cited by the Examiner FOREIGN PATENTS UNITED STATES PATENTS 929,795 6/ 1963 Great Brtan. 'g'' C tflg; gg ROBERT A. OLEARY, Primm Examiner. 2,818,860 1/1958 Holm et al. '12S-191 D MEYER PERLIN, Examiner.

2,925,722 2/1960 Blackburn et al. 62-5'14 X 3,102,777 9/1963 Bedrosian et a1. N' RWILSONASS'mmExamme 

1. APPARATUS FOR CONTROLLING THE OXYGEN CONCENTRATION IN THE ATMOSPHERE IN A COMPARTMENT MEANS, COMPRISING: COMPARTMENT MEANS ADAPTED TO THE PASSAGE OF GASEOUS ATMOSPHERES THEREINTO AND THEREFROM, EQUIPMENT MEANS OPERABLE TO REFRIGERATE SAID COMPARTMENT MEANS, INERT GAS MATERIAL SOURCE STORAGE MEANS FOR STORING A SUPPLY OF INSERT GAS MATERIAL OTHER THAN OXIDES OF CARBON, TO PROVIDE A SOURCE OF INERT GAS MATERIAL OTHER THAN OXIDES OF CARBON, PASSAGE MEANS HAVING AN INLET MEANS COMMUNICATING WITH THE INTERIOR OF SAID SOURCES STORAGE MEANS AND AN OUTLET MEANS COMMUNICATING WITH THE INTERIOR OF SAID COMPARTMENT MEANS TO ALLOW PASSAGE OF SAID INERT GAS MATERIAL FROM THE INTERIOR OF SAID SOURCE STORAGE MEANS AND OUT OF SAID OUTLET MEANS INTO THE INTERIOR OF SAID COMPARTMENT MEANS TO BECOME PART OF SAID ATMOSPHERE IN SAID COMPARTMENT MEANS, VALVE MEANS IN SAID PASSAGE MEANS, OXYGEN SENSING MEANS IN SAID COMPARTMENT MEANS FOR SENSING THE OXYGEN CONCENTRATION IN SAID ATMOSPHERE IN SAID COMPARTMENT MEANS, VALVE CONTROL MEANS RESPONSIVE TO SAID OXYGEN SENSING MEANS AND CONNECTED TO CONTROL SAID VALVE MEANS, WHEREBY SAID VALVE MEANS IS ACTUATED TO PERMIT SAID INERT GAS MATERIAL TO FLOW FROM SAID SOURCE STORAGE MEANS INTO THE INTERIOR OF SAID COMPARTMENT MEANS TO BECOME PART OF SAID ATMOSPHERE THEREIN WHEN SAID OXYGEN SENSING MEANS SENSES OXYGEN IN SAID ATMOSPHERE IN SAID COMPARTMENT MEANS AT A CONCENTRATION ABOVE A PREDETERMINED VALUE AND TO PREVENT THE FLOW OF SAID INERT GAS MATERIAL FROM SAID STORAGE MEANS INTO THE INTERIOR OF SAID COMPARTMENT MEANS WHEN SAID OXYGEN SENSING MEANS SENSES OXYGEN IN SAID ATMOSPHERE IN SAID COMPARTMENT MEANS AT A CONCENTRATION BELOW SAID PREDETERMINED VALUE. 